This invention relates to gas turbine engines used to provide thrust for aircraft. In particular, the present invention relates to thrust reversers used with turbofan gas turbine engines.
Typical aircraft turbofan engines include a fan that draws and directs a flow of air into a nacelle and into and around an engine core. The nacelle surrounds the engine core and helps promote the laminar flow of air around the core. The flow of air that is directed into the engine core is initially passed through a compressor that increases the air flow pressure, and then through a combustor where the air is mixed with fuel and ignited. The combustion of the fuel and air mixture produces a flow of exhaust gas that causes a series of turbine blades at the rear of the engine core to rotate, and to drive the engine's rotor and fan. The high-pressure exhaust gases from the combustion of the fuel and air mixture are thereafter directed out of the engine through an exhaust nozzle at the rear of the engine.
Bypass flow is air that is directed around the engine core. In turbofan engines, the bypass flow typically provides the main thrust for an aircraft. The bypass flow also can be used to help slow a landed aircraft. Thrust reversers mounted in the nacelle structure selectively reverse the direction of the bypass flow to generate reverse thrust. During normal engine operation, the bypass flow may or may not be mixed with the engine core exhaust before exiting the engine assembly.
Thrust reverser systems are used in aircraft engines to slow the velocity of the aircraft during a landing. Typical thrust reverser systems include blocking devices that are fashioned to articulate from an outer duct wall of a bypass duct. The blocking devices need to be positioned when the aircraft is in flight so that normal bypass flow to the final exit of the engine is not impeded. During thrust reversal, blocking devices change position to block flow through the bypass duct and direct the bypass airflow through an opening in the outer wall of the duct to produce reverse thrust. The blocking devices move from one position to another as a result of a movement of a translating sleeve which moves in an aft direction to open a passage for reverse thrust airflow during a thrust reversal. Reduction of aero drag in a bypass duct is a major target for improving engine fuel burn efficiency. One candidate for reduction of aero drag is elimination or reduction of drag links that are used to move the blocking elements of a thrust reverser. These drag links radially cut and split the bypass flow and produce turbulence in the bypass duct. The problem is that drag links have proven to be very effective for passively and synchronously deploying blocker elements as a result of imparted translating sleeve motion.
Another type of thrust reverser makes use of a pivot door reverser, which replaces the translating sleeve with pivot doors which flip open to create an exit passage through both the outer duct wall and the nacelle outer barrel. This eliminates any translating elements. The pivot door reverser dumps bypass air outward and forward to achieve the reverser flow vectors. The forward portion of the pivot door is configured to seal the outer duct during cruise operation. The aft portion of the pivot door is shaped to achieve a close fit with the core cowl when the pivot door is deployed to its full pivoted thrust reversal position to block through flow of bypass air. The required seals for the pivot door reverser tend to be problematic, and the pivot door requires that there be an opening in the outer barrel of the nacelle so that the forward part of the pivot door can extend outward of the outer barrel during thrust reversal.